Add builds to the docs as a valid skip option for backups.

doc/raketasks/backup_restore.md

@@ -29,7 +29,7 @@ sudo -u git -H bundle exec rake gitlab:backup:create RAILS_ENV=production
 ```
 
 Also you can choose what should be backed up by adding environment variable SKIP. Available options: db,
-uploads (attachments), repositories. Use a comma to specify several options at the same time.
+uploads (attachments), repositories, builds(CI build output logs). Use a comma to specify several options at the same time.
 
 ```
 sudo gitlab-rake gitlab:backup:create SKIP=db,uploads